(c) A. Lobel/NASA/Spitzer Space Telescope/IRAC
An
international team of professional and amateur astronomers, which
includes Alex Lobel, astronomer at the Royal Observatory of Belgium, has
determined in detail how the temperature of four yellow hypergiants
increases from 4000 degrees to 8000 degrees and back again in a few
decades. They publish their findings in the professional journal
Astronomy & Astrophysics.
The researchers analysed the light of four yellow hypergiants that
has been observed on Earth over the past fifty to one hundred years.
Yellow hypergiants are huge, luminous stars. They are fifteen to twenty
times heavier than the Sun and shine 500,000 times brighter. The
atmospheres of these stars can be so huge that, if they replaced our
Sun, they would stretch beyond the orbit of Jupiter.
Because the researchers had such a long series of measurements, they
could see in detail how the stars get warmer over decades and cool down
in a few years.
The cycle begins with a cool star. In a few decades, the average
atmospheric temperature increases to about 8000 degrees. At 8000
degrees, however, the atmosphere becomes unstable due to amplified
pulsations. At a certain moment the entire atmosphere erupts. As a
result, it cools down quickly and a self-accelerating process occurs in
which electrons attach themselves to hydrogen ions and a lot of
ionisation energy is released. This cools the atmosphere even further.
The cooling from 8000 degrees to 4000 degrees takes only two years.
Then the cycle starts again from the beginning, only with a slightly
less massive star. Eventually, astronomers think, the hypergiant
transforms into a hotter star and ends its life as a supernova.
During the research, astronomers also found out that one of the four studied hypergiants was not as large as previously assumed. The star, HR5171A, turns out to be much closer than expected.
Source: Royal Observatory of Belgium
Contact:
Alex Lobel
E-mail: alex.lobel@oma.be
Phone number : +32(0)23730348
See also: http://alobel.freeshell.org/hr5171.html
Article:
A.M. van Genderen et al. (2019), Pulsations, eruptions and evolution of four yellow hypergiants. Accepted for public ation in Astronomy & Astrophysics:https://doi.org/10.1051/0004-6361/201834358. Free preprint: http://arxiv.org/abs/1910.02460
